Ok jur it took me awhile, but I understand WHY you think the bottom spokes are doing the work. Your logic is that if the top spokes where bearing the load the rim would collapse from the top right? because they would fail from being overloaded right?

But that is precisely why the rims do not collapse from the top. Because the TOP spokes ARE SUPPORTING. rims collapse from the bottom because those spokes are NOT SUPPORTING. The rim will collapse from the WEAKEST point. The bottom.

Also take into account that if spokes are laced radially, that diminishes greatly the bottom spokes ability to support.